Hydrocarbons Hydrocarbons are molecules which contain hydrogen and carbon
There are many different compounds that can form with carbon and hydrogen
There are 3 main hydrocarbon families
Alkane
Alkene
Alkyne

Where do you find hydrocarbons? Carbon compounds make up 90% of all chemical compounds and many form the basis of living systems
The majority of hydrocarbons found naturally occur in crude oil
Crude oil forms from decomposed organic matter which has lots of carbon and hydrogen!.
Proteins, carbohydrates and fats
all contain carbon, hydrogen and
oxygen

1. Alkanes Are hydrocarbons that contain only carbon and hydrogen
They only have single bonds
CnH2n + 2
A series of compounds with similar properties in which each member differs from the previous one by –CH2 is known as a homologous series
Structural formulas show the number and location of bonds but not lone pairs

Straight and branched chain A straight-chain is where the carbon atoms in an alkane, alkene and alkyne form a chain that runs from one end of the molecule to the other.
A branched chain is were an alkane, alkene and alkyne has alkyl groups bonded to its central carbon chain.
An alkyl is a group of atoms consisting of carbon and hydrogen atoms, arranged in a chain.

Naming isomers 1. Name and number longest carbon chain (circle it)
2. Identify branches (there are no branches at ends!)
3. Name each branch (alkyl group) put them in alphabetical order
methyl CH3 ethyl C2H5 propyl C3H7 butyl C4H9
pentyl C5H11
4. If there is more than 1 alkyl group use:
di = 2, tri = 3, tetra = 4 as a prefix e.g. diethyl, trimethyl
5. Write the number of the carbon atom each alkyl group is attached to. Put commas between numbers if there is more than one alkyl group (2,3-dimethyl)
6. Put hyphens between numbers and words (2,2 – dimethylbutane)

Saturated compounds A saturated compound has no double or triple bonds.
In saturated linear hydrocarbons, every carbon atom is attached to two hydrogen atoms, except those at the ends of the chain, which have three hydrogen atoms.
In the case of saturated methane, four hydrogen atoms are attached to the single, central carbon atom.
Of simple hydrocarbons, alkanes are saturated, and alkenes are unsaturated.

Physical Properties of Alkanes and Alkenes As the number of carbon atoms increases in a homologous series there is a change in the physical properties
At room temperature, the lighter alkanes and alkenes are gases; the midweight alkanes are liquids; and the heavier alkanes are solids, or tars.
Why?
London forces increase as molecules get heavier

Volatility Volatile liquids are those that evaporate (go from liquid to solid) easily.
Smaller molecules are more volatile
Why?
Because there are weak London forces so it is easier for them to go from a liquid to a gas

Viscosity Viscosity is the measure of the thickness of a fluid
Honey is more viscose (it is harder to pour) than water
The larger the molecule the more viscous it is
The larger the molecule the stronger the London forces which means they are more likely to stick together because they are long they get tangled up like spaghetti

Hydrocarbon Solubility The rule to use when determining hydrocarbon solubility is: Like dissolves like.
This means that polar compounds (water, and alcohols) dissolve other polar compounds.
Nonpolar compounds dissolve other nonpolar compounds but tend not to dissolve polar compounds.

Reaction with bromine solution Ethene reacts with bromine and bromine is added to the ethene molecule. Ethene loses its double bond
This is called an addition reaction because bromine is added to ethene

Reaction with bromine solution This is used to test for unsaturation
If the solution is unsaturated the red brown colour of bromine disappears
The red brown colour disappears becasue the bromine becomes part of the ethene molecule
Permanganate solution is also used to test for unsaturation

Test for unsaturation Bromine does not react with an alkane because the alkane contains only single C-C bonds which cannot add the bromine. Alkanes merely dilute the red-brown bromine color to an orange or yellow color
Due to their C=C double bonds which can be broken, alkenes react readily with bromine to produce saturated dibromoalkanes.